Binder for preforms in silencers

ABSTRACT

In a method of forming a silencer preform from fibers of a fiberizable material, the fibers are fed into a mold, and a low temperature cure binder is applied to the fibers. The binder is cured at a low temperature to bond together the fibers, thereby forming a preform having generally the shape of the mold. The preform is removed from the mold. The preform is structured for insertion into a silencer. A silencer preform includes fibers of a fiberizable material and a low temperature cure binder bonding together the fibers.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

This invention relates in general to fiber preforms and in particular to preforms for use in silencers such as mufflers or other automotive exhaust components.

BACKGROUND OF THE INVENTION

It is common to include sound absorbing material in automotive exhaust components to dampen or attenuate the acoustic energy contained in engine exhaust gases as they pass from the engine through the exhaust system to the atmosphere. Frequently glass fiber preforms are used as the sound absorbing material.

Preforms for automotive exhaust components are often made by texturizing a continuous strand of glass fibers (separating the strand into individual filaments), feeding the fibers into a mold, and applying a binder to the fibers as they are texturized or after they are in the mold. The binder is cured at an elevated temperature to bond the fibers together, thereby forming a more or less rigid preform having the shape of the mold. The temperature of the binder and preform is typically raised to the curing temperature by blowing hot air into the fibers or placing the preform with uncured binder into an oven. The heating process can require significant capital investment as well as significant amounts of energy, and it can increase the cycle time required for making the preform.

German Patent Application No. 06.1092.4.wz discloses a fiber preform for use in an automotive exhaust component comprising glass fibers bonded together by a phenolic resin binder. Carbon dioxide is applied to the binder during the curing process to allow curing with minimal heating.

Japanese Patent Publication No. 06-143272 discloses a fiber preform production method. Chopped glass fibers, a polyester resin and a curing agent are sprayed together onto a mold. The resin is then cured at room temperature.

U.S. Pat. No. 3,927,139 discloses a method of fabrication of resin bonded fiber reinforced articles by a spray-up technique. The articles are formed by spraying a catalyst-liquid resin mixture onto chopped glass fibers. The resin is rapidly cured at room temperature.

U.S. Pat. No. 6,426,121 discloses a dual cross-linkable polymer binder suitable for use in preparing products from a non-woven web material. The binder is curable at room temperature.

U.S. Pat. No. 5,766,541 discloses a method of making a fiber preform for use in an automotive muffler by feeding glass fiber strands and a binder into a perforated mold, and blowing heated air through the mold to cure the binder.

SUMMARY OF THE INVENTION

The invention relates to a method of forming a silencer preform from fibers of a fiberizable material. The fibers are fed into a mold. A low temperature cure binder is applied to the fibers. The binder is cured at a low temperature to bond the fibers together, thereby forming a preform having generally the shape of the mold. The preform is removed from the mold. The preform is structured for insertion into a silencer.

The invention also relates to a silencer preform. The preform comprises fibers of a fiberizable material, and a low temperature cure binder bonding the fibers together. The preform is structured for insertion into a silencer.

Various additional aspects of the invention will become apparent from the drawings and the detailed description and preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preform that can be made according to the invention.

FIG. 2 is a perspective view of a perforated mold that can be used to make the preform.

FIG. 3 is a perspective view of the preform inserted into the shell of an automotive muffler.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

In contrast to known preforms for use in silencers, the preforms of the invention are made with a binder that can be cured at a low temperature in a relatively brief time. This can significantly reduce capital and energy costs and the cycle time required to make the preforms.

The preforms can be used to make any type of silencer. As is well known, silencers are components or devices which function to dampen or attenuate acoustic energy (sound). They often include an outer shell or housing and a preform which fits inside the shell/housing. The silencers are often used as part of a larger system or apparatus. Some systems or apparatuses that may include silencers are automotive exhaust systems, diesel and gas engines, compressors, high pressure gas release systems, blowers, vacuum pumps, vents/blowoffs, and gas turbines.

By “low temperature cure binder”, as used herein, is meant a binder that can be substantially completely cured (hardened to form a stable material) at or near room temperature. For example, the curing temperature may be not greater than about 50° C., and typically within a range of from about 17° C. to about 35° C.

The binder can be cured in a relatively brief period of time, such as a time of not greater than about 30 minutes. For example, the cure time may be not greater than about 20 minutes, not greater than about 15 minutes, or within a range of from about 1 to about 10 minutes.

The binder may be curable at the low temperature without applying to the binder a nonbinder material that does not become part of the final binder. For example, as discussed below, a binder comprising a mixture of a resin and a curing promoter is one embodiment of the invention. However, the binder may be curable at the low temperature without applying to the binder a gaseous curing promoter, such as carbon dioxide.

The curing may be done without applying heat, such as heated air or electromagnetic radiation, to the binder. However, in some instances heat or some type of electromagnetic radiation may be applied to further speed up the curing process.

Any suitable low temperature cure binder, or a mixture of different binders, can be used in the invention. The binder may comprise a single material or multiple materials. For example, the binder may comprise a low temperature curing resin. In one embodiment, the binder comprises a resin in combination with a material that promotes curing of the resin, such as an activator, catalyst, or setting/hardening agent. The curing promoter may be a liquid, emulsion, or particulate solid when mixed with the resin, which becomes part of the final cured binder on the fibers of the preform. A liquid curing promoter is used in one embodiment. The resin and the curing promoter may be applied separately to the fibers to avoid having the resin cure before bonding together the fibers to form the preform, although they may also be applied together.

Any suitable resin, or a mixture of different resins, can be used in the binder. Some nonlimiting examples of resins that may be suitable include alkaline modified phenolic resins that may be combined with ester setting agents, epoxies that may be combined with amine setting agents, melamines that may be combined with acid setting agents, polyurethanes, furans, and urea formaldehydes.

Some particular examples of alkaline modified phenolic resins are the ALPHASET® series of resins manufactured by Hexion Specialty Chemicals, Columbus, Ohio (formerly Borden Chemical). For example, the ALPHASET 9010, 9020, 9030 and 9040 resins may be suitable for use in the binder. The different resins of the series differ somewhat in their viscosity, solids content and other properties. The ALPHASET® resins derive their alkalinity primarily from added sodium hydroxide or potassium hydroxide. The ALPHASET® resins are disclosed in U.S. Pat. Nos. 4,424,467 and Re. 32,812. Hexion also manufactures the BETASET® (alkaline modified phenolic resins) and the SIGMASET® (phenolic urethanes) series of resins that may be suitable for use in the binder.

The ALPHASET® resins can be combined with an ester setting/hardening agent in the binder to promote curing of the resin. For instance, Hexion manufactures the ALPHACURE® series of liquid ester setting/hardening agents, such as ALPHACURE 103, 104 and 105.

The ratio of the resin to the curing promoter in the binder will depend on the particular compositions and process conditions. For instance, different combinations of resin and curing promoter can produce different cure rates suitable for different methods of application and molding techniques. In some embodiments, when the resin is an alkaline phenolic resin and the activator is an ester, the resin and the ester may be used in a ratio within a range of from about 2:1 to about 10:1, or from about 3:1 to about 5:1.

The amount of the binder applied to the fibers will also depend on the particular compositions and process conditions. The binder is applied in an amount sufficient for bonding the fibers together in the finished preform, and to supply sufficient mechanical integrity to the preform. The preform maintains its shape during its subsequent use, for example, during its insertion into a muffler shell in a muffler assembly operation. The binder may be applied relatively uniformly throughout the fibers or applied mainly to the surfaces of the preform. In some embodiments, the binder is applied in an amount within a range of from about 1% to about 30% by weight of the final preform, from about 1% to about 20%, from about 2% to about 10%, or from about 2% to about 5%.

The silencer preforms are often manufactured and/or used in applications where they are exposed to relatively high temperatures. For the safety of workers and users, the binder may be substantially nontoxic such that when the preform is heated to a temperature of 250° C., for example in a muffler installed on a vehicle, the binder emits not greater than the OSHA permissible exposure limits of toxic gases.

Any suitable fiberizable material, or a mixture of different fiberizable materials, can be used to make the fibers of the preforms. For example, methods and compositions for making mineral fibers such as glass fibers or basalt fibers, polymer fibers, carbon fibers, asphalt fibers, and mixtures of these fibers are known in the art. The fibers are able to withstand the thermal, mechanical and chemical conditions present in the sound attenuating device into which the preform is inserted.

The fibers can have any suitable form, such as continuous fibers, fibers cut into lengths of several centimeters or more, or chopped fibers typically of length less than 4 centimeters and/or fibers of several centimeters in length such as those produced in a mineral wool or AF glass wool process. The fibers may be produced by attenuating fiber forming material in a fiber-forming apparatus such as a spinner, bushing or orifice plate, although they may also be made by any other suitable method. The filaments may be coated with a sizing composition comprising functional agents such as lubricants, coupling agents and film-forming polymers, during the fiber production process. Chopped or cut fibers can be made by cutting strands into discrete length fibers with a chopper or similar device well known in the art. Fibers made by a wool process can also be coated with some type of sizing materials and subsequently coated with the low temperature cure binder for use in the preform. The fibers used in the preform may be texturized, by any suitable method, to increase their sound attenuation/damping properties, although non-texturized fibers may also be used.

The binder can be applied to the fibers by any suitable method. It can be applied either before or after the fibers have been fed into the mold. For example, it can be applied during the fiber texturizing or chopping process. The binder can be applied in any suitable manner, such as spraying, brushing, dip coating or curtain coating. For example, one method is to separately but simultaneously spray a liquid resin and a liquid setting agent in small droplet form onto the fibers as or shortly after the fibers are texturized.

A binder or a portion of the binder having a relatively high viscosity may present difficulties during the application of the binder to the fibers. For instance, a resin having a relatively high viscosity may be difficult to spray, which may result in the sprayer producing a narrow stream of the binder instead of a dispersed mist that can be applied relatively uniformly throughout the fibers. Thus, in some embodiments of the invention, at least a portion of the binder is applied to the fibers using pressurized application equipment such as a pressurized spray system.

Alternatively, or in addition to using the pressurized equipment, a viscosity modifier can be added to at least a portion of the binder to facilitate its application to the fibers. For instance, a viscosity reducer such as potassium hydroxide or other known materials can be added to a relatively viscous resin to reduce its viscosity.

The binder often tends to adhere to materials as it cures. If the binder adheres to the mold surface, it may make the preform difficult to remove from the mold and/or contribute to build-up on the mold. Thus, in some embodiments of the invention a release agent is applied to the mold to prevent or decrease these problems. Any suitable release agent can be used, such as silicones or Teflon®-containing materials.

Any suitable mold and related apparatus can be used in the invention. In some embodiments, the mold is perforated, especially when compressed air is used to texturize the fibers before they are fed into the mold and/or to apply the binder to the fibers. U.S. Pat. No. 5,766,541, which is incorporated by reference herein, describes a perforated mold and related apparatus for making fiber preforms. Another perforated mold is described hereinbelow and shown in FIG. 2. However, unperforated molds are also suitable in some embodiments of the invention.

When the preform is removed from the mold, the preform is structured for inclusion as part of the silencer. In some embodiments, the preform is sized and shaped to substantially fill an interior cavity of a shell or housing of the silencer, such as the shell of a muffler, while leaving room for any associated components devices, such as exhaust pipes, baffles, or perforated tubes that are associated with mufflers. Alternatively, multiple preforms can be used to fill the interior cavity of the silencer. The preforms can be sized and shaped so as to fit any portion of a silencer.

Referring now to the drawings, FIG. 1 shows a preform 10 that can be made according to the invention. The preform includes fibers 10 a held together by a binder 10 b. The preform is sized and shaped to substantially fill an interior cavity of a muffler shell. The preform has three holes 12, 14 and 16 extending through it to allow pipes associated with the muffler to pass through the preform.

FIG. 2 shows a mold 18 that can be used to make the preform 10. The mold includes an oblong-shaped solid bottom end 20. Three cylindrical tubes 22, 24 and 26 are attached to the bottom end of the mold and extend perpendicularly therefrom. In the embodiment shown, the tubes are hollow and have perforated cylindrical surfaces and solid top ends. The tubes of the mold correspond to the holes of the preform.

The mold also includes an outer shell 28. In the embodiment shown, the outer shell comprises perforated first and second shell halves 28 a and 28 b. The shell halves are pivotable about a hinge 30 at one end of the shell, for opening and closing the outer shell. The outer shell includes clamps 32, 33 and 34 at the other end of the shell for fastening closed the shell halves. The interior of the closed outer shell defines a cavity having the approximate size and shape of an interior cavity of a muffler shell.

The mold further includes an oblong-shaped solid top 36. The top 36 of the mold has three holes 38, 40 and 42 to allow the top ends of the tubes 22, 24 and 26 to pass therethrough when the top is installed on the mold. The top includes flanged bars 44 and 46 on its ends that abut the end of the outer shell to facilitate the positioning of the top onto the mold. The top 36 may be designed to fit inside the mold shell 28 so that the sound absorbing material in the mold can be compressed to a given height determined by tabs (not shown) on the inside of the mold shell.

The mold can be made out of a variety of materials since it does not have to be heated to above near room temperature in order for the binder to be cured. Making the mold out of material which would be resistant to the binder sticking to the mold (e.g. Teflon®) could make removal of the preform from the mold more efficient. In addition, portions of the mold (e.g. the tubes) or the entire mold could be made of an elastomeric material which would allow the size and shape of the mold to be changed for easy removal of the preform.

Owens Corning sells Silentex® machines which are typically used to fill mufflers or preform molds or bags with texturized fiberglass materials. This type of machine uses as input material a fiberglass strand containing several thousand individual fibers. The strand passes through a nozzle into which compressed air is introduced. The compressed air serves to separate the individual filaments so that they will more efficiently attenuate acoustic energy. In addition, the compressed air helps to move the texturized strand out of the nozzle and into whatever type of container is to be filled. In this invention, the binder could be supplied to the nozzle so that two streams of liquid could be introduced into the nozzle after the material is texturized or could be applied to the texturized material immediately after exiting the nozzle and applied to the texturized strand before or as the strand enters the mold. The texturized strand coated with the binder may be directed into the mold in a manner which ensures uniform filling of the mold without negatively impacting the quality of texturization of the strand. One or more dimensions of the mold may be reduced after the texturized material is introduced into the mold so that the preform will be of the proper size that it can easily be installed in a silencer.

FIG. 3 shows the preform 10 inserted into the shell 48 of an automotive muffler 50. It is seen that the preform substantially fills the interior cavity of the muffler shell, although such is not necessary.

One skilled in the art will appreciate that the invention is not limited to the particular methods and compositions described herein, and that changes can be made without departing from the scope of the invention, which is defined in the appended claims. 

1. A method of forming a silencer preform from fibers of a fiberizable material comprising the steps of: feeding the fibers into a mold; applying a low temperature cure binder to the fibers before or after the fibers are fed into the mold; curing the binder at a low temperature to bond together the fibers thereby forming the preform having generally the shape of the mold; and removing the preform from the mold, the preform being structured for insertion into a silencer.
 2. The method of claim 1 wherein the curing is done without applying heat to the binder.
 3. The method of claim 1 wherein the curing is completed in a time of not greater than about 20 minutes.
 4. The method of claim 1 wherein the binder is cured at a temperature not greater than about 35° C.
 5. The method of claim 1 wherein the binder is applied in an amount within a range of from about 1% to about 20% by weight of the final preform.
 6. The method of claim 1 wherein the binder is substantially nontoxic, such that when the preform is heated to a temperature of 250° C., the binder emits not greater than the OSHA permissible exposure limits of toxic gases.
 7. The method of claim 1 wherein the binder comprises a resin and a curing promoter.
 8. The method of claim 7 wherein the curing promoter is a liquid.
 9. The method of claim 7 wherein the resin comprises an alkaline modified phenolic resin.
 10. The method of claim 7 wherein the resin and the curing promoter are applied separately to the fibers.
 11. The method of claim 1 wherein at least a portion of the binder is applied to the fibers using pressurized application equipment.
 12. The method of claim 1 comprising an additional step of adding a viscosity modifier to at least a portion of the binder before applying the portion to the fibers.
 13. The method of claim 1 wherein the mold is perforated.
 14. The method of claim 1 wherein the mold is made partially or entirely of elastomeric material.
 15. The method of claim 1 comprising an additional step of applying a release agent to the mold prior to feeding the fibers into the mold.
 16. The method of claim 1 wherein the fiberizable material comprises glass.
 17. The method of claim 1 wherein the fibers are texturized.
 18. The method of claim 1 wherein the silencer is a component of an automotive exhaust system.
 19. A method of forming an automotive exhaust preform from fibers of a fiberizable material comprising the steps of: feeding the fibers into a mold; applying a low temperature cure binder to the fibers before or after the fibers are fed into the mold; curing the binder at a temperature not greater than about 50° C. and for a time of not greater than about 20 minutes, and without applying heat to the binder, to bond together the fibers thereby forming the preform having generally the shape of the mold; and removing the preform from the mold, the preform being structured for insertion into an automotive exhaust component.
 20. A silencer preform comprising: fibers of a fiberizable material; and a low temperature cure binder bonding together the fibers to form the preform; the preform being structured for insertion into a silencer.
 21. The preform of claim 20 wherein the automotive exhaust component is a muffler. 